Historically, [1]} found that the total iron mass in the ICM is proportional to the total luminosity of the early type galaxies in the clusters. And the IMLR in the B-band had larger values in clusters than in groups, mainly caused by the biased low early global abundance measurements (see §REF ) at the group scale [2]}, [3]}.
The current state of the art of measurements of the IMLRs is achieved by combining near-infrared (K-band) luminosities [4]}, [5]} obtained with the two micron all sky survey (2MASS) and the measurements performed by Suzaku extending to the outer regions of nearby clusters and groups [6]}, [7]}, [8]}. Figure REF  reports the IMLRs thus obtained: there is a general increase with radius and poorer clusters and groups also have lower IMLRs within the 0.2 \(r_{180}\)  region. On the other hand, the IMLRs of groups and clusters in the outer region at \(r>0.5~r_{180}\)  seem to be closer to each other. Figure REF  suggests that poorer systems (groups and clusters with fewer member galaxies) could not hold the gas including metals due to the relatively shallower potential in their assembly process. In a following work [9]} showed that the same systems have lower IMLRs and larger entropy excess, which is a signature of the non-gravitational energy input in the central regions of groups during the assembly stage.
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